Accurate Optical Observation of Space Objects in LEO Regime

2017

Observations of space objects in high altitude regimes (MEO and GEO) are normally done by means of passive optical sensors (telescopes). Accuracy of the astrometric data down to 1 arcsecond is achievable with appropriate sensor hardware, observation strategies and suitable image data processing pipelines. Considering the diurnal, meteorological and Earth shadow constraints but also the higher relative angular velocities when observing objects at closer orbits, passive optical means traditionally becomes less suitable for LEO regimes, however the practical experience and the challenge trying to maintain this accuracy and performance tracking at lower orbits with modified optical sensors, taking into account better time registry and carefully evaluating some parameters as trailing losses and optimal exposure times among others, provides interesting results and opportunities for optimized LEO optical sensors as well. A review of the impact of the main aspects is provided in this paper ...

Italian Air Force (ITAF) recognizes the relevance of a sensor architecture for a Space Surveillance & Tracking (SST) capability to protect its own space and satellite assets and infrastructure against the damage or destruction from collision with other space debris in orbit. In 2011, the Italian Government has delegated the ITAF, with collaboration of Italian Space Agency (ASI) and National Institute for Astrophysics (INAF), to study the feasibility of a national architecture using already existent assets and processing capabilities for SST. It was started a survey at national level and an experimentation using radar sensors, property of ITAF and INAF, both in monostatic and bistatic configuration. In 2014, the European Commission, with the Decision 541/2014/EU of 16th April, established an European SST framework, to promote the use of national assets and processing capabilities of Members State. Those national capabilities have to guarantee an initial European Architecture to provide an SST Services with the huge challenge of gradually becoming self-sufficient and independent in producing an integrated European space surveillance network. The national contribution to European architecture will be composed of both radars and optical sensors since they have different capability and provide complementary type of information regarding targeted object. Collected data from networked sensors will be sent to a national integration centre in order to analyze it and make the orbit determination of the detected space debris using specific software tools. In this paper we briefly describe the potential capabilities of these sensors and the results of preliminary tests carried out separately with a monostatic long range radar and an optical telescope managed by Italian Air Force (ITAF) for the detection of a subset of space objects in LEO orbit with the perspective to perform a sensor data fusion experiment in the near future. In particular, the optical sensor is a telescope properly designed for SST and is able to observe the portion of space above it with a coverage of 360°x90° in azimuth and elevation. The telescope is equipped with two CCD sensors: one with a wide field of view used for surveillance tasks and the second with a narrow field dedicated for tracking specific objects. The sensor is managed by an operating software system that allows user to remotely plan and schedule its daily activity and to make orbit determination and collision risk assessment in a completely automated way.

Advances in Space Research, 2011

Under ESA contract an industrial consortium including Aboa Space Research Oy (ASRO), the Astronomical Institute of the University of Bern (AIUB), and the Dutch National Aerospace Laboratory (NLR), proposed the observation concept, developed a suitable sensor architecture, and assessed the performance of a space-based optical (SBO) telescope in 2005. The goal of the SBO study was to analyse how the existing knowledge gap in the space debris population in the millimetre and centimetre regime may be closed by means of a passive optical instrument. The SBO instrument was requested to provide statistical information on the space debris population in terms of number of objects and size distribution. The SBO instrument was considered to be a cost-efficient with 20 cm aperture and 6°field-of-view and having flexible integration requirements. It should be possible to integrate the SBO instrument easily as a secondary payload on satellites launched into low-Earth orbits (LEO), or into geostationary orbit (GEO). Thus the selected mission concept only allowed for fix-mounted telescopes, and the pointing direction could be requested freely. Since 2007 ESA focuses space surveillance and tracking activities in the Space Situational Awareness (SSA) preparatory program. Ground-based radars and optical telescopes are studied for the build-up and maintenance of a catalogue of objects. In this paper we analyse how the proposed SBO architecture could contribute to the space surveillance tasks survey and tracking. We assume that the SBO instrumentation is placed into a circular sunsynchronous orbit at 800 km altitude. We discuss the observation conditions of objects at higher altitude, and select an orbit close to the terminator plane. A pointing of the sensor orthogonal to the orbital plane with optimal elevation slightly in positive direction (0°a nd +5°) is found optimal for accessing the entire GEO regime within one day, implying a very good coverage of controlled objects in GEO, too. Simulations using ESA's Program for Radar and Optical Observation Forecasting (PROOF) in the version 2005 and a GEO reference population extracted from DISCOS revealed that the proposed pointing scenario provides low phase angles together with low angular velocities of the objects crossing the field-of-view. Radiometric simulations show that the optimal exposure time is 1-2 s, and that spherical objects in GEO with a diameter of below 1 m can be detected. The GEO population can be covered under proper illumination nearly completely, but seasonal drops of the coverage are possible. Subsequent observations of objects are on average at least every 1.5 days, not exceeding 3 days at maximum. A single observation arc spans 3°to 5°on average. Using a simulation environment that connects PROOF to AIUB's program system CelMech we verify the consistency of the initial orbit determination for five selected test objects on subsequent days as a function of realistic astrometric noise levels. The initial orbit determination is possible. We define requirements for a correlator process essential for catalogue build-up and maintenance. Each single observation should provide an astrometric accuracy of at least 1"-1.5" so that the initially determined orbits are consistent within a few hundred kilometres for the semimajor axis, 0.01 for the eccentricity, and 0.1°for the inclination.

The aspects of optical observations of space debris (SD) in Low Earth Orbit (LEO) are considered. This problem is studied at the present time for LEO SD much less comparing to High Earth Orbit (HEO) and, particularly, geostationary orbits. Preferable regions of the celestial sphere for LEO SD observation in a survey mode are localized by modelling passes of catalogued SD through the telescope's coverage area, and taking into account the conditions of optical visibility. The dependence of these area characteristics on local time, season of observation, and latitude of telescope location are studied. The results can represent a practical interest for the development of efficient strategies for LEO SD searching, planning the observation campaigns, analysis of the obtained measurement data, and validation of the SD models, based on the optical observations.

2014

In this paper we present the results from the coverage and the orbit determination accuracy simulations performed within the recently completed ESA study “Assessment Study for Space Based Space Surveillance (SBSS) Demonstration System” (Airbus Defence and Space consortium). This study consisted in investigating the capability of a space based optical sensor (SBSS) orbiting in low Earth orbit (LEO) to detect and track objects in GEO (geosynchronous orbit), MEO (medium Earth orbit) and LEO and to determinate and improve initial orbits from such observations. Space based systems may achieve better observation conditions than ground based sensors in terms of astrometric accuracy, detection coverage, and timeliness. The primary observation mode of the proposed SBSS demonstrator is GEO surveillance, i.e. the systematic search and detection of unknown and known objects. GEO orbits are specific and unique orbits from dynamical point of view. A space-based sensor may scan the whole GEO ring ...

2019

In 2018 the 6 Remote Observatories for Asteroid and Debris Searching (6ROADS) and the Astronomical Observatory of Adam Mickiewicz University (AO AMU) performed a joint observing campaign of low LEO objects – very fast targets, difficult to observe for optical SST sensors. Two small, highly automatic telescopes have been used during the campaign: 0.7m RBT/PST2 in USA (AO AMU) and 0.4m Solaris Observatory in Poland (6ROADS). We present the analysis of astrometric data collected during the campaign, which includes the quality of objects’ orbital parameters, determined from observations, as a function of the observation arc length, number of astrometric observations and force models taken into account in orbit determination. In particular, the influence of the atmospheric drag perturbations is analyzed in terms of the applied atmospheric model and the area to mass A/M ratio of the observed object.

Acta Astronautica, 2014

Understanding of the space debris environment and accuracy of its observation-validated models are essential for optimal design and safe operation of satellite systems. Existing ground-based optical telescopes and radars are not capable of observing debris smaller than several millimeters in size. A new experimental and instrumental approachthe space-based Local Orbital Debris Environment (LODE) detectoraims at in situ measuring of debris with sizes from 0.2-10 mm near the satellite orbit. The LODE concept relies on a passive optical photon-counting time-tagging imaging system detecting solar photons (in the visible spectral range) reflected by debris crossing the sensor field of view. In contrast, prior feasibility studies of space-based optical sensors considered frame detectors in the focal plane. The article describes the new experimental concept, discusses top-level system parameters and design tradeoffs, outlines an approach to identifying and extracting rare debris detection events from the background, and presents an example of performance characteristics of a LODE sensor with a 6-cm diameter aperture. The article concludes with a discussion of possible sensor applications on satellites.

2013

The increasing amount of space debris requires the satellite operators to handle a growing number of collision risk assessments in order to eventually perform collision avoidance manoeuvrers. For this scheme to work effective and reliable, the acquisition of highly accurate orbital position data of detected threatening space debris is necessary. The successful experimental demonstration of our earlier published concept on laser-based distance measurements of space debris in low earth orbits has proven this technique to be feasible for this task. Hereby a powerful short pulse laser system within a ground-based transceiver set-up is used to measure the time-of-flight of the back-scattered laser pulse from the space debris object. The time-of-flight information ultimately correlates with the object distance. A passive optical tracking unit equipped with a highly sensitive camera system is used for initial localisation and coarse determination of the debris position to guide the laser t...

2009

This paper focuses on the features of optical observations of space debris (SD) in Low Earth Orbit (LEO) in a survey mode. These issues for LEO are at present time studied much less comparing to High Earth Orbit (HEO) and, particularly, geostationary orbits. Preferable regions of celestial sphere for LEO SD observation in a survey mode are localized by modeling passes of catalogued SD through the telescope’s coverage area and taking into account the conditions of optical visibility. The dependence of these area characteristics on local time, season of observation and latitude of telescope location are studied. The results can represent practical interest for development of the efficient strategies for LEO SD searching, planning the observation campaigns, analysis of the obtained measurement data and validation of the SD models based on the optical observations.

2019

The Faculty of Mathematics, Physics and Informatics of Comenius University in Bratislava, Slovakia (FMPI) has been developing its 70 cm Newtonian design telescope (AGO70) since 2016 within the framework of the ESA Plan for Cooperating States (PECS) programme for Slovakia. The ongoing development is performed for space debris tracking situated from Low Earth Orbit (LEO) to Geosynchronous Earth Orbit (GEO) and is focused on the improvement of hardware, system control software, image processing software and the observation program. The AGO70 has been installed at the FMPI’s Astronomical and Geophysical Observatory in Modra, Slovakia (AGO) in Fall 2016. It was a standard astronomical system capable to perform measurements of e.g. stellar objects, near Earth asteroids, comets, etc. To achieve that the system could be effectively used for space debris research and space surveillance tracking (SST), there were several predefined objectives to be accomplished. First, the hardware, e.g., tel...